Recent development of information-oriented society has popularized mobile communication equipment such as portable phones and portable information terminals. The portable phones use an RF band such as a 800 MHz-1.0 GHz band and 1.5 GHz-2.0 GHz band. Accordingly, a duplexer that utilizes an acoustic wave such as a surface acoustic wave filter (SAW filter) or a film-bulk acoustic resonator (FBAR) are used. It is also considered to use another type of duplexer using a boundary acoustic wave filter.
The recent portable phones have progressed to multiple bands and multiple modes, and are further equipped with an additional radio interface such as wireless LAN or GPS. In the above situation, the duplexer is demanded to have improvements in size and performance. Particularly, the duplexer is desired to achieve both downsizing and reliable isolation between pads.
There is proposal to provide a shield electrode between patterns of multiple SAW filters and to thus improve the isolation characteristics (see Japanese Laid-Open Patent Publication No. 2006-60747). There is another proposal to prevent interference between signals by arranging input and output terminals for making external connections so as to diagonally connect corners of the shape of a device having multiple filter elements (see Japanese Laid-Open Patent Publication No. 2002-76829).